1. Technical Field
The present invention relates to an apparatus for adjusting balance, a method for adjusting balance, and a method for assembling a disk, which are used to achieve the rotating balance of a disk in a hard disk drive or the like.
2. Description of the Related Art
A disk drive, such as a hard disk drive, has a circular plate-like disk for recording data. The disk is held on a spindle and driven to rotate by a spindle motor. A read/write head accesses an area on the disk surface to read the recorded data and write data onto the disk. In such a disk drive, if the disk is eccentric with respect to the spindle, deflection of rotation is caused when the disk rotates, and as a result, an access error or the like due to the read/write head may occur to reduce the accuracy of reading and writing data. Such eccentricity is caused by displacement of the disk in the radial direction thereof with respect to the center of rotation of the spindle in the range of the clearance formed between the inner peripheral surface of the disk""s center hole and the outer periphery of the spindle.
The rotating balance of a disk is classified into two types, static balance and dynamic balance. The static balance is a balance against the vibration component comprising a translational force caused in the disk rotation, and it is influenced by the radial eccentricity of the disk with respect to the center of rotation. The dynamic balance is a balance against the vibration component by the torque (torsional moment) caused when an object rotates, and it is influenced not only by the radial eccentricity of the disk with respect to the center of rotation, but also by displacement of the center of gravity of the disk in the axial direction of the spindle.
If the spindle is provided with only one disk, the thickness of the disk (size in the axial direction of the spindle) is small as compared with the disk diameter, and thus the influence of the dynamic balance is negligibly small as compared with the influence of the static balance. Even if the spindle is provided with a plurality of disks, the influence of the dynamic balance can also be ignored, provided that the setting range of the disks provided on the spindle (setting distance between the disk at one end and the disk at the other end) is short and the spindle is also short. However, as the number of disks provided on the spindle becomes large and the setting range of the disks provided on the spindle becomes large, the effect of the dynamic balance becomes so large that it cannot be ignored. In particular, as the storage capacity demanded in the hard disk drive or the like has recently been larger and larger, the number of disks provided on the spindle tends to increase. Further, since the number of revolutions of the disk also tends to increase to accelerate the access speed, it is needed to accurately adjust dynamic balance as well as static balance.
There has been a technique for adjusting static balance and dynamic balance by attaching a weight to a system comprised of disks and a spindle. For instance, to provide dynamic balance, as shown in FIG. 6, the balance of a spindle 2 provided with a predetermined number of disks 1 is measured, and a weight 3 is attached to both ends of the spindle 2 as needed. However, in this approach, the attaching of the weight 3 is time-consuming, and the balance must be adjusted before the disks 1 and the spindle 2 can be assembled on a base 4. Thus, limitations are imposed on the manufacturing process, and it is not an efficient approach.
The present invention is based on such a technical problem, and its object is to provide an apparatus for adjusting balance, a method for adjusting balance, and a method for assembling a disk, which can adjust dynamic balance reliably and efficiently.
In connection with the foregoing, as a technique for enabling the modification of balance with the disk and the spindle being assembled on the base, the applicant has already proposed the technique disclosed in Japanese Published Unexamined Patent Application No. 9-161394.
In this technique, the spindle is inserted into the center hole of the disk, and after temporarily fixing the disk to the spindle, an acceleration is provided to the spindle in the radial direction of the disk. Then, the disk stands still because of the inertial force by its own weight, and only the spindle skids in the radial direction thereof, by which the eccentricity of the disk is adjusted. And, after the rotating balance of the disk falls within a predetermined accuracy, the disk is permanently fixed to the spindle. By this, static balance can be provided efficiently and reliably.
Further, to adjust dynamic balance with this technique, as shown in FIG. 7, with an arrangement in which a spindle 2 having a predetermined number of disks 1 is set on a base 4, acceleration is given to the base 4 in the radial direction of the disks 1 by actuators 5A and 5B. In this case, the base 4 supports one end (lower end) of the spindle 2 at its bottom 4a. And, to the side wall 4b of the base 4 which is provided so as to surround the outer periphery of the predetermined number of disks 1, acceleration is provided at both the lower and upper ends thereof by the actuators 5A and 5B, thereby to provide acceleration to the two ends of the spindle 2, respectively. Allowing for the overall unbalance of the predetermined number of disks 1 provided on the spindle 2, dynamic balance is adjusted by making the accelerations acting on one end and the other end of the spindle 2 differ from each other.
For instance, to adjust the position of the disks 1 with respect to the center of rotation thereof only on the top end 2a side of the spindle 2, a force is applied to the base 4 only by the actuator 5A. FIG. 8A shows a dynamical model for this. If, in this model, it is assumed that the distance from the center of gravity G of a system comprising the disks 1, spindle 2, and base 4 to the upper end of the spindle 2 is h, and a force F is applied by the actuator 5A at a position at a distance L from a line passing through the center of gravity G and perpendicular to the axis of the spindle 2, then a distributed acceleration a(x) is observed on the axis of the spindle 2. This acceleration a(x) is obtained as follows. The overall translational acceleration aG is expressed by:
aG=F/M 
The rotating angular acceleration (around the center of gravity is G) is expressed by the following equation, where M is the overall mass, and I is the rotation moment with respect to the center of gravity G:
axe2x88x92LF/I 
Thus, the composite acceleration a(x) is expressed by the following equation, whose distribution is as shown in FIG. 8B:
a(x)=aG+ax=F(1/M+Lx/I) 
As obvious from this figure, if only the upper actuator 5A is operated, a large acceleration is applied to the disk 1 on the upper end side of the spindle 2, and the disk 1 on the upper end side can be selectively skidded. Further, if the distance L is selected so as to fulfill the following expression, it is possible to zero the acceleration provided to the disk 1 on the lower end side of the spindle 2, as shown in FIG. 8C:
(1/Mxe2x88x92Lx/I)=0 
However, the careful examination of the above technique by the present inventors shows that the effect as desired cannot be obtained as a matter of fact. The reasons for that are as follows.
1) Since the system comprising the base 4 and the spindle 2 has a very high rigidity, the acceleration provided by the actuator 5A to the upper portion of the spindle 2 is also applied to the lower portion of the spindle 2.
2) If acceleration is provided on a jig 6 only by the upper actuator 5A, it is also applied to the lower end of the side wall 4b of the base 4 by a plate 7 provided between the actuators 5A and 5B and the side wall 4b of the base 4.
3) As shown in FIG. 8D, since the base 4 is set on the jig 6, if acceleration is applied, for instance, by the actuator 5A, a counterforce xe2x80x9cxe2x88x92axe2x80x9d of the rotating angular acceleration a caused by it is generated.
For these reasons, the result as desired above cannot be obtained through prior art designs.
The apparatus for adjusting balance of the present invention, which was based on such examination, is an apparatus for adjusting balance of the rotating system of a disk drive which rotatively drives a disk provided on a spindle, the rotating system including at least the disk, characterized in that there are provided for the spindle a plural pairs of both a displacement detector for detecting the radial displacement component of the rotating system when the rotating system is rotated, and an accelerator for providing the spindle with an acceleration in the direction substantially perpendicular to the axis of the spindle through a retainer member for retaining the spindle or an adapter member detachably fixed to the spindle, and in that each pair of the displacement detector and the accelerator comprises a controller for controlling the acceleration provided by the accelerator according to the detected result in the displacement detector.
With such configuration, if, in each of the plural pairs of the displacement detector and the accelerator which are provided for the spindle, acceleration is applied to the spindle by the accelerator controlled by the controller according to the detected result in the displacement detector, the disk stands still because of the inertia by its own weight, and only the spindle moves. As a result, the positional relation between the disk and the central axis of the spindle changes, so that the balance for the center of rotation of the rotating system including the disk can be adjusted. At this point, to the spindle, acceleration from the accelerator of each pair is provided through the retainer member or the adapter member. With this, acceleration from the accelerator of each pair is directly inputted in a direction substantially perpendicular to the axis of the spindle from the position at which the accelerator of each pair is provided.
If the spindle and the disk integrally rotate, the rotating system are made up of these two, and, if only the disk rotates relative to the spindle, the rotating system consists only of the disk. The present invention is applicable to any case.
Further, the adapter member of this apparatus for adjusting balance can be characterized in that it is detachably fixed to the spindle by a bolt screwed into a tapped hole previously provided in the spindle. If a tapped hole for attaching a cover for the disk and the spindle is previously formed in the spindle, the adapter member can be attached by the use of this tapped hole, and any special process is not needed to attach the adapter member.
Further, the present invention may be an apparatus for adjusting balance comprising a plurality of actuators comprised of a piezoelectric element or the like, each driven upwardly in the vertical direction for applying acceleration to a rotator, which is set with the rotating center shaft thereof being substantially horizontal, at least at one end and the other end of the rotating center shaft, a sensor for detecting the rotating balance when the rotator is rotated, and a controller for controlling the acceleration applied to the rotator by each actuator according to the detected result at the sensor. Also, with such apparatus for adjusting balance, the eccentricity of the rotator with respect to the center of rotation can be eliminated to adjust the rotating balance by applying acceleration to one end and the other end of the rotating center shaft.
However, differently from the present invention, with the configuration in which acceleration is applied horizontally from the side to a rotator with the rotating center shaft thereof being substantially vertical, an abrasion resistance is produced between the floor and the rotating center shaft when acceleration is applied to move the rotating center shaft.
On the other hand, the present invention has a configuration in which acceleration is applied by actuators driven upwardly in the vertical direction to a rotator with the rotating center shaft being substantially horizontal, providing the apparatus for adjusting balance with a so-called vertical configuration. With such configuration, when acceleration is applied to the rotating center shaft by actuators, the rotating center shaft does not receive abrasion resistance between the floor and the rotating center shaft and the applied acceleration directly acts on the rotating center shaft to carry out the modification with good accuracy.
In this case, acceleration is not always applied to both one end and the other end of the rotating center shaft, but it may be applied to either of them depending on the amount of unbalance of the rotator. Further, by the existence of an acceleration transmitter between one end and the other end of the rotating center shaft and each actuator, the acceleration applied by the actuators can be directly transmitted to the rotating center shaft with reliability.
The method for adjusting balance of the present invention is characterized by comprising a step of detecting the displacement of a spindle while disks are rotating, a step of determining the accelerations to be provided to the spindle, a step of providing the respectively determined accelerations to the spindle through a retainer for retaining one end and the other end of the spindle, and a step of determining whether or not the displacement of the spindle after provided with the accelerations is equal to or smaller than a predetermined threshold value. With such a configuration, accelerations can be provided to one end and the other end of the spindle depending on the deflection of the dynamic balance of the disks to adjust it to be equal to or smaller than the predetermined threshold value. To one end and the other end of the spindle, accelerations are directly inputted from the position at which the retainer is provided.
The present invention may be a method for adjusting balance in which, after measuring the amount of unbalance for the center of rotation when a plurality of disks held by a spindle is rotated, either one end or the other end of the spindle or both are struck based on the measured amount of balance, thereby to adjust the amount of unbalance. Thus, by striking either one end or the other end of the spindle or both, the positions of the disk with respect to the center axis of the spindle can be adjusted to reduce the amount of unbalance. Further, by previously pressing one end and the other end of the spindle in the direction opposite to the direction of the strike by a pressing means, respectively, the shock by the strike can be made to positively act on the spindle.
The method for assembling a disk of the present invention can be characterized by having a first step of retaining both ends of a spindle by a retainer while the disk is temporarily fixed to the spindle inserted into the center hole of the disk, a second step of charging the positional relation between the disk and the center axis of the spindle by providing the spindle with acceleration in the direction perpendicular to the axis of the spindle through the retainer, and a third step of permanently fixing the disk to the spindle when the unbalance of the disk for the center axis of the spindle becomes equal to or smaller than a predetermined threshold value. Thus, the adjustment of unbalance of the disk can be efficiently performed in assembling process.
Further, by performing the adjustment of unbalance while the disks and the spindle are set on the base, the manufacturing process can be made more efficient. Furthermore, when providing acceleration to the spindle, the need for providing an additional motor or the like is eliminated by rotating the disk with a drive source provided in the spindle itself.